5D question on ISO/noise

Question for fellow 5D owners. Since i only upgraded from a Rebel a few months ago, im still pretty tentative/hesitant to use high ISOs (400+) with my 5d, even though supposedly noise supposedly isnt too bad even at 800+ (??) I really don't want to try dozens of test shoots, so is there a way to predetermine when to expect noise to appear, for example how long an exposure at a certain ISO will result in noise appearing? Does the aperature value make any difference? Thanks for any info!

Stan,

I'm not a 5D owner, but I think I can answer at least part of your question.

The visible noise is a factor of the signal to noise ratio. The noise generated on a chip is basically constant. The brighter the image or the more light energy captured, the greater the signal component will be. By turning up the ISO, you are amplifying the signal from the sensor prior to the A/D converter, but this also amplifies the noise component.

For the most part, you'll be able to minimize noise at a given ISO in your images by exposing to the right and then lowering exposure in post processing if you need to. This nets the highest signal to noise ratio for a given ISO.

You'll always notice that the noise is most prominent in dark areas of the photograph, areas which generate the least amount of signal.

I can't tell you the exact point where the 5D images will fall apart.

I think that's exactly the info i was looking for, Mel, so thanks--what i was wondering is whether slightly overexposing ( or bracketing to the right) might help minimize noise, and it sounds like that might help.

Yes it will. I hope I did justice explaining the basic mechanics as to why.

This is different than the other reason why we expose to the right. The other reason, probably the main reason we do it, is because in digital we get more differentiating values for colors in the higher numeric values than we get in the lower numeric values. So half the possible colors are in the first stop of brightness, one quarter in the next stop, one eight in the next stop, etc...

Mel-

Stan, above ISO 800 the answer to your question starts getting a bit subjective.
How much does the noise bother you?

Pixel peeping at 100% can make it look bad.
Do you anticipate a large print, or just viewing on screen?
Is there a lot of shadow detail that you need to recover ?
Is there a lot of detail that you don't want to lose by using noise reduction software?
What is your processing workflow? Does it enhance detail, along with noise?
etc.

On the 1DsMk2, I don't hesitate using ISO 800, when needed (wildlife in poor light).
I'll go above that as a last resort.
The 5D has slightly better noise response - but probably not a whole stop?

I shoot a lot of night time sports and am constantly requiring ISO 800-1600. Even then, the noise isn't too bad. Only if I need to enlarge a print to 16x20, or more, do I feel that using noise reduction SW (Noise Ninja or Neat Image) is prudent. Using the noise reduction SW is really quite amazing, so I wouldn't let high ISO bother you - just use it as needed, not for everyday use...

Ken

I have used my 5D at the high ISO setting, 3200. I haven't found the noise too bad. There are 2 noise settings on the camera. One runs through the entire files trying to find and eliminate noise. I believe that most of the D-SLR's have this feature. There is also a setting that evaluates the file for noise and cleans it up where required. The first feature takes as long to run through as the picture took to take, or at least I am told it does. I use the second setting and have had some interesting experience when shooting long exposures with Nikon shooters. I don't hesitate to shoot at ISO 800. I use ISO 1600 when I have to, like trying to capture a moving animal in low light conditions, where the options are use the higher ISO settings or don't get the shot. I have occasionally had to go to ISO 3200 to get the shot. I have used ASA 400 and 800 films that had more noise (grain) than I get at ISO 3200. (I'm dating myself)

Stan, I would advise to try it and see what you get. Film for the 5D is real cheap, so fire away. I think that this is the only way that you can finds your comfort level. I haven't reached the point where I need to use Noise Ninja or Neat Image, but that is definitely an option to be looked into.

Bill- "yes" to all of the above Everyone-thanks for the advice/info, it was very helpful!

While we're on this subject...I've been wondering something about ultra long exposures with digital cameras. I don't know a lot of tech terms you use so if you could keep in it simple...thanks. I like to take startrail shots (with film), which depending on what you want can take up to four hours on bulb. My question is, is it the ISO that creates noise..the higher it is the more noise, or is it the length of an exposure? If high ISO creates noise then if you take startrail shots at ISO 100 (as I would with film) would there be little noise and look like it was shot with a low speed film? Hope someone can help...

Thanks for any answers.

Cynthia,

ISO "creates" noise, or I should say it increases the ratio of noise to signal. With the night sky, the sky should be black, and this is the part that shows noise the worst.

But long exposures generate heat within the chip that can also contribute to noise. Doing this in cold weather is probably the best option.

What you are thinking of would probably look fine at ISO 100, similar to ISO 100 film, but without the reciprocity failure issues. But you'll get more details at ISO 400 or higher.

Cynthia, obviously im not the expert, but i would say "both". As heat builds up there's gonna be noise in a long exposure. I dont think there's any way you can escape noise in a really long exposure with digital regardless of ISO (beyond maybe 10 minutes for example). I know some pure digital shooters try to compensate for this problem by taking multiple successive exposures and then blending them, but that's not a very satisfactory solution, obviously.
Edit: i see Mel beat me to the punch--guess i gotta work on my typing speed